This invention relates, in general, to ribbon sensing apparatus and more particularly to circuitry used in conjunction with an end-of-ribbon sensor device for providing an indication of when the ink ribbon remaining on the supply spool has been depleted to a predetermined amount, such as the end portion.
In various commercially available typewriters and other data printing machines employing an ink ribbon in the printing process, it is normally desirable to provide means to indicate when the ink ribbon is essentially depleted from the supply spool. This requirement is more important when a matrix-type plastic ribbon is used rather than a cloth ribbon since the plastic ribbon is used only one time during the printing function. With the advent of the electronically controlled automatic text-editing typewriter employing a ribbon cartridge, it is even more important to provide such indicating means. Without some type of indication or control regarding the amount of ink ribbon remaining on the supply spool, a portion of a line or page could be automatically typed without the benefit of an ink ribbon.
It has been known to employ various types of physical pins or clips attached to the ribbon near the end of the ribbon supply to either physically move a lever or to provide electrical contact to sense the end portion of the ribbon remaining on the ribbon supply. It is also known to employ rod or lever means, which project through an opening in the ribbon supply hub upon the depletion of the ribbon on the ribbon supply spool, to sense the end portion of the ribbon. In addition, it is known to employ a lever or follower which contacts the outer periphery of the ink ribbon on the supply spool and through its pivotal motion during the depletion of the ink ribbon, signals the occurrence of the end portion of the ribbon on the ribbon supply spool. The previously discussed types of sensing mechanisms have been implemented in machines having an ink ribbon mechanism consisting of a ribbon supply spool and a ribbon take up spool mounted on opposite sides of the machine rather than being contained within a ribbon cartridge.
With machines employing the moving carriage with a ribbon cartridge mounted thereon, a smaller and less mechanically complex type of sensing mechanism is desired which may be mounted on the carriage for movement therewith. It would also be desirable to have the end-of-ribbon sensor be free of physical contact with the ribbon and thereby eliminate the problem of having the end-of-ribbon sensor become a factor in the determination of ribbon drive force or ribbon tension force required for the ribbon system. Presently, there is marketed a serial printer which employs a movable carriage with the ribbon cartridge and the daisy wheel print element mounted thereon. When an end-of-ribbon sensor is embodied in such an existing printer, which is presently embodied in a commercially available automatic text editing typewriter, it is desirable to provide such a sensor without requiring a significant redesign of the carriage and associated elements. When positioning an end-of-ribbon sensor on or attached to the moving carriage, which includes the ribbon cartridge, the sensor should not restrict the motion of the carriage or associated elements or cause appreciable dynamic problems due to its mass or friction. If the sensor is of the optical type, the sensor should function properly with different types of ribbons and different colors of ribbon and function properly under various light conditions normally found in the office environment. It is also desirable that the end-of-ribbon sensor provide an indication that the end of the ribbon is near but provide the indication at a point which allows the present line of typing to be completed prior to stopping the printer.
Circuitry associated with the end-of-ribbon sensor should provide a reliable and positive signal indicating the presence of the end portion of the ribbon.
Accordingly, it is a primary object of the present invention to provide improved circuitry to be used with an end-of-ribbon sensor with the circuitry providing a positive indication of the presence of the end of the ribbon.
Another object of this invention is to provide improved circuitry which incorporates components to introduce delay and comparison features to improve reliability of the indication of the end of the ribbon.
A further object of the present invention is to provide capability of sampling of the indication of the end-of-ribbon at specific times to improve reliability of the indication.
Other objects and advantages will be evident from the specification and claims when read in conjunction with the accompanying drawing illustrative of the invention.